After loss of renal mass, the remaining renal tissue compensates with an increase in growth and function. We propose to investigate the regulation of the compensatory adaptation. We will test the hypothesis that the regulation occurs via humoral growth factors and will attempt to isolate and characterize the factors. We will also test the hypothesis that the cellular membrane is a key component in the regulation of renal compensatory adaptation. We propose to answer the following specific questions: 1. What factors in the serum or kidney initiate renal compensatory adaptation? 2. What factors in the kidney or serum inhibit renal growth? 3. How do these factors regulate adaptation, especially in regard to their action on cellular membranes? 4. When do the factors disappear from the serum and kidney when optimal compensatory adaptation is attained? 5. Do the initiating factors accelerate renal adaptation during conditions where it is depressed, for example during starvation? We will compare the unknown initiating factors with certain known factors. These include high protein and ammonium chloride feeding. 6. What is the relationship between protein, phospholipid, and enzyme production and turnover during membrane biogenesis in the kidney? Our long term goal is to understand the regulation and augmentation of renal cellular growth and regeneration. Hopefully, the findings can be applied to the achievement of optimal renal function in patients following renal injury.